The present invention relates to a hydraulic frictional device or element which is used in a power train of an automatic transmission in the form of a multiple plate clutch or a multiple plate brake.
A service manual entitled "NISSAN FULL RANGE ELECTRONICALLY CONTROLLED AUTOMATIC TRANSMISSION OF THE RE4R01A TYPE" published in Japan in March 1987 shows on pages I-79 to I-83 a plurality of such hydraulic frictional devices of the above kind. The hydraulic frictional devices use a hydraulic working fluid for cooling a set of interleaved friction plates. In order to effectively cool the friction plates, an arrangement is made to splash the hydraulic fluid onto the plates or immerse the plates in the hydraulic fluid.
Heat is generated and accumulated in each of the friction plates owing to frequent repetition of engagement and release cycle or sliding engagement over a prolonged period of time. The amount of heat accumulated to one of the plates is determined by its heat capacity. If this heat capacity is low, therefore, the plates are liable to be baked.
An object of the present invention is to improve a hydraulic frictional device of the above kind such that heat accumulated in one of the friction plates is effectively dissipated without any major modification of the hydraulic frictional device.